Recommends Procedures For Inspection Of Nuts And Bolts Through The Rear Spar

The FAA has released a Special Airworthiness Information Bulletin (SAIB) for Air Tractor, Inc. Models AT-401B, AT-402B, AT-502A, AT-502B, AT-504, AT-602, AT-802, and AT-802A having serial numbers prior to 401B/402B-1347, 502A/502B-3059, 504-4029, 602-1278, and 802/802A-0661 airplanes (under Type Certificate Data Sheets A17SW and A19SW)

The SAIB follows an in-flight failure of the bolts at the vertical fin rear spar attach connection, which caused the rudder boost trim mounting bracket to migrate out of its normal position. Following the failure, Air Tractor, Inc. issued Snow Engineering Co. Service Letter (SL) #359, Revision A. The FAA says that to date, there have been two failures of these bolts. Failure of these bolts may lead to difficulty controlling the airplane. The SL specifies instructions for replacement of the nuts and bolts through the vertical fin rear spar attach point.

The FAA recommends that the affected owners of the Air Tractor airplanes referenced in the Introduction section of this SAIB replace the six bolts and nuts through the vertical fin rear spar with NAS1303 bolts and MS21042-3 nuts at the next annual inspection using the procedures in SL #359, Revision A, dated November 29, 2017. Before the next flight, the FAA also recommends that affected owners remove the surrounding skin to visually inspect both the forward and aft sides of the bolts for damage. The FAA recommends that any findings of damaged bolts be reported to the FAA.

(Image from file)

FMI: SAIB